Telemetering system for oil wells

ABSTRACT

An acoustic communication method and system for transmitting information through a well bore drill string or other pipe by establishing in the pipe modulated torsional acoustic waves, preferably of zero order, which contain the information to be transmitted and travel from a signal transmitting station to a signal receiving station spaced along the pipe, and for demodulating the modulated waves arriving at the receiving station to recover the transmitted information. The modulated waves may be established in the pipe either by driving the pipe in torsional oscillation and modulating the resulting torsional waves in the pipe at the transmitting station or by launching modulated torsional waves through the pipe at the transmitting station. In its principal application, the invention is utilized to monitor selected well drilling parameters, such as temperature, formation pressure, formation porosity, drill string orientation, and/or to operate devices within the well bore. Primary advantages of the invention are reduced acoustic transmission losses from acoustic coupling to the drilling fluid and well bore wall and the ability to transmit information while drilling is in progress. According to the preferred practice of the invention, when monitoring drilling parameters, the torsional acoustic waves are launched downwardly through the drill string from the surface by exciting the upper end of the string in a zero order torsional acoustic oscillation at frequencies within the base band of the drill string acoustic transmission characteristics so as to minimize attenuation of the acoustic waves by the couplings between the drill string pipe sections. These torsional acoustic waves are modulated at a subsurface signal-transmitting station along the drill string and returned back through the string to a surface signal-receiving station where the modulated waves are demodulated to recover the transmitted information.

Elite Lamel et al.

tates atent 1 TELEMETERING SYSTEM FOR OIL WELLS Inventors: Arthur E.Lamel, Arcadia; William D. Squire; Harper .1. Whitehouse, both of SanDiego, all of Calif.

[21] Appl. No.: 113,147

[56] References Cited UNITED STATES PATENTS 2,161,256 6/1939 Karcher73/151 3,520,375 7/1970 Raynal et a1... 175/50 3,205,477 9/1965 Kalbfell340/18 NC 3,633,688 1/1972 Bodine.... 175/56 3,475,722 10/1969 White340/15.5 SW 2,658,578 11/1953 Oliphant 340/155 SW 3,588,804 6/1971 Fort340/18 LD 3,252,225 5/1966 Hixson 340/18 NC OTHER PUBLICATIONS Barnes etal., Passbands for Acoustic Drill String," pg. 1606-1608, S.A.S.A., Vol.51, No. 5 (Part 2).

McSkimir, Measurement of Torsional Waves, 7/22/52, pg. 355-364,S.A.S.A., Vol. 24 No. 4.

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-N. MoskowitzAttorney, Agent, or Firm-Forrest .l. Lilly [57] ABSTRACT An acousticcommunication method and system for NC, 340/18 LD, 340/l3.5 51L;

181/.5 AG, 175/40, 166/113 [51] Int. Cl G01v 1/114 [58] Field ofSearch... 340/18 LD, 15.5 SW, 18 NC;

transmitting information through a well bore drill string or other pipeby establishing in the pipe modulated torsional acoustic waves,preferably of zero order, which contain the information to betransmitted and travel from a signal transmitting station to a signalreceiving station spaced along the pipe, and for demodulating themodulated waves arriving at the receiving station to recover thetransmitted information. The modulated waves may be established in thepipe either by driving the pipe in torsional oscillation and modulatingthe resulting torsional waves in the pipe at the transmitting station orby launching modulated torsional waves through the pipe at thetransmitting station. lln

.its principal application, the invention is utilized U to monitorselected we drilling parameters, I s ren as temperature, formationpressure, formation porosity, drill string orientation, and/or tooperate devices within the well bore. Primary advantages of theinvention are reduced acoustic transmission losses from acousticcoupling to the drilling fluid and well bore wall and the ability totransmit information while drilling is in progress. According to thepreferred practice of the invention, when monitoring drillingparameters, the torsional acoustic waves are launched downwardly throughthe drill string from the surface by exciting the upper end of thestring in a zero order torsional acoustic oscillation at frequencieswithin the base band of the drill string acoustic transmissioncharacteristics so as to minimize attenuation of the acoustic waves bythe couplings between the drill string pipe sections. These torsionalacoustic waves are modulated at a subsurface signal-transmitting stationalong the drill string and returned back through the string to a surfacesignal-receiving station where the modulated waves are demodulated torecover the transmitted information.

TELEMETERING SYSTEM FOR OIL WELLS BACKGBOUND OF THE INVENTION RelatedApplicationsi: Q, j g HM I This application is a parent of copendiiigapplications filed September 12, 1973, under Serial Nos. 396,400,396,401, 396,403, and 396,411.

' 1. Field of the Invention MW This invention relates generally to theart of transmitting telemetric and control information through a hollowwell bore drill string or other pipe. More particularly, the inventionrelates to an improved acoustic communication method and system for thepurpose described wherein the information carrier is provided bytorsional acoustic waves preferably of Zero order.

2. Description of the Prior Art As will appear from the ensuingdescription, the present acoustic communication method and system may beemployed to transmit information between two points of any pipe havingan intervening length capable of sustaining torsional acoustic waves,particularly torsional waves of zero order. However, the principalapplication of the invention involves transmission of telemetric andcontrol information through a hollow drill string suspended within awell bore. Accordingly, the invention will be disclosed in connectionwith this particular application.

When drilling a well bore, it is desirable, if not essential, to monitorselected drilling parameters in the vicinity of the drill bit for thepurpose of providing the drilling operator with sufficient informationto properly control the drilling operation. Among the drillingparameters which provide valuable information to the drilling operatorare temperature, formation pressure, formation porosity, and others. Inslant drilling operations, such as off-shore drilling of multiple wellsfrom a single platform or island, an additional drilling parameter whichprovides extremely valuable, if not essential information to thedrilling operator, is drill string orientation.

Such drill string orientation is expressed in terms of the azimuth andpitch or inclination of the lower end of the string and must beaccurately measured at frequent intervals during the drilling operationin order to maintain the proper slant drilling direction.

At the present time the most widely used method of measuring drillstring orientation involves the use of a well log which is lowered on acable through the hollow drill string to the bottom of the well bore.This log contains instruments, such as a compass and a spirit level orpendulum, for sensing drill string azimuth and inclination and a camerafor photographically recording the instrument readings. After actuationof the camera to record these instrument readings, the log is withdrawnfrom the drill string and the film is developed to obtain the readings.While this method provides accurate information concerning drill stringorientation, it is extremely time-consuming and substantially increasesthe total drilling cost. Thus, each well logging operation involvescessation of drilling, uncoupling the drilling kelly from the drillstring, lowering and subsequently raising the log the whole length ofthe drill string, recoupling the kelly to the drill string, andresumption of the drilling operation. In many off-shore drillingoperations, periodic logging of the well bore in this fashion mayaccount for up to one-half the total drilling time and hence for a largeportion of the total drilling cost.

The present invention proposes to avoid the above and otherdisadvantages of the described well logging technique and to improve onthe existing techniques for monitoring other drilling parameters byproviding a novel acoustic communication method and system fortransmitting telemetric and control information through a drill string.As will appear from the later description, such information transmissionmay occur while the drill string is stationary or rotating.

The prior art relating to well drilling is replete with position orstation along the drill string to recover the transmitted information.In the present disclosure, the station from which the modulated acousticwaves propagate is referred to as a signal-transmitting station. Theposition at which the modulated waves are demodulated to recover thetransmitted information is referred to as a signal-receiving station.

The prior acoustic communication systems for transmitting informationthrough a drill string are deficient in that they utilize relativelyinefficient modes of acoustic wave propagation and thus achieve, atbest, only marginal information transmission. In this regard, it issignificant to note that most published patents in the field use suchdescriptors as vibrations, sound, acoustic waves, and the like, todescribe the acoustic information carrier, and do not specificallydefine the exact mode of acoustic wave propagation. Those patents whichdo describe a specific form of acoustic wave propagation utilize eitherlongitudinal or flexural vibration modes. These latter vibration modes,however, are ill suited for use in transmitting information through adrill string owing to the large transmission losses which occur as aresult of acoustic coupling of the drill string to the drilling fluidand the wall of the well bore.

Because of these large transmission losses, the patented drill stringcommunication systems are at best capable of operation only in a mannerwherein the acoustic waves are modulated and launched upwardly throughthe drill string from a signal-transmitting station at the lower end ofthe string to a signal receiving station at the surface. This manner ofoperation requires installation of the acoustic wave transducer and itselectronic driving circuitry within the lower end of the drill string.Accordingly, the transducer and circuitry must be designed to fit theenvelope of the drill string and to survive the hostile environmentexisting within the lower end of the well bore during drilling. Inaddition, servicing and replacement of the transducer and its circuitryrequires removal of the entire drill string from, and subsequentlowering of the entire drill string into, the well bore.

SUMMARY OF THE INVENTION ceiving station are demodulated to recover thetransmitted information. It is significant to note here that theinvention contemplates within its scope two different methods ofestablishing the modulated acoustic waves within the drill string.According to one method, acoustic waves are first established in thedrill string and these waves are modulated at the signal transmittingstation by exciting an acoustic wave modulator in the drill string witha modulating signal representing the information to be transmitted.According to the other method, modulated acoustic waves containing theinformation to be transmitted are generated in the drill string at thesignal transmitting station by exciting an acoustic wave generator ortransducer in the drill string with a driving signal which is modulatedto represent the information to be transmitted. Accordingly, it will beunderstood that within the context of the present disclosure, terms suchas modulate, modulation, cover both modulation of existing acousticwaves in the drill string and generation or launching of modulatedacoustic waves into the drill string for the purpose of establishing inthe drill string modulated acoustic waves containing the information tobe transmitted.

Telemetric signals transmitted through the drill string may representselected drilling parameters in the vicinity of the drill bit, such astemperature, formation pressure, formation porosity, drill stringorientation, and others. In this case, modulation occurs at a subsurfacesignal-transmitting station adjacent the lower end of the drill stringwith telemetric signals from sensors responsive to the selected drillingparameters to be monitored. Control signals transmitted through thedrill string may be utilized to operate, from a station on the drillingplatform, devices within the well bore, such as signal transmitterslocated at sub-surface stations along the drill string.

One important aspect of the invention is concerned with the form ofacoustic waves which are employed to transmit information. According tothis aspect, the waves are torsional acoustic waves. Such torsionalacoustic waves are superior to all other acoustic waves, such aslongitudinal and flexural, for information transmission through a drillstring in that they couple less acoustic energy into the drilling fluidand wall of the well bore and thus permit efficient signal transmissionthrough a greater length of drill string. In its broader scope, theinvention contemplates the use of any torsional acoustic waves which maybe launched through a drill string and modulated to transmit informationthrough the string. However, the preferred waves are torsional acousticwaves of zero order, that is, torsional acoustic waves characterized bypure rotation of the drill string about its central axis. Such zeroorder torsional waves are non-dispersive, i.e., the velocity of thewaves is independent of their frequency, while most other acoustic waveforms are dispersive. Nondispersive wave propagation through a drillstring is highly desirable and often essential to rapid signaltransmission through the string for the reason that dispersion smearsthe information signals modulated'on the waves.

Another important aspect of the invention involves the direction oftorsional wave propagation through the drill string. According to thisaspect of the invention, the torsional acoustic waves may be launcheddownwardly through the drill string from the surface or upwardly throughthe drill string from the lower end of the string. In the preferredpractice of the invention involving transmission of telemetric signalsrepresenting selected drilling parameters, the torsional acoustic wavesare luanched downwardly through the drill string from the surfacedrilling platform to a subsurface signal-transmitting station at thelower end of the drill string. The waves arriving at the lowertransmitting station are modulated with the telemetric signals to bemonitored and returned back through the drill string to a signalreceiving station at the drilling platform where the modulated waves aredemodulated to recover the transmitted signals. This method of wavepropagation is permitted because of the above-described reduction inacoustic transmission losses which results from the use of torsionalacoustic waves, particularly torsional waves of zero order whosefrequencies lie within the base band of the drill string acoustictransmission characteristics. Such a propagation method is preferred forthe reason that the torsional wave generator, comprising a transducerand its electronic driving circuitry, may be located out of the wellbore at the drilling platform. The torsional wave generator is therebyisolated from the hostile environment in the well bore and is readilyaccessible for repair and servicing without removal of the drill string.Also, the drill string envelope imposes no constraint on the size andarrangement of the generator. However, it is considered to be within thescope of the invention to launch the torsional waves upwardly throughthe drill string from a subsurface signal-transmitting station.

In those applications involving transmission of control signals throughthe drill string from a signaltransmitting station at the drillingplatform to a subsurface signal-receiving station along the drillstring, the torsional waves are preferably launched downwardly throughthe drill string from the surface. Here again, however, it is consideredto be within the scope of the invention to launch waves upwardly throughthe drill string from its lower end, modulate the waves at the surfacesignal-transmitting station with the control signals to be transmitted,and return the modulated waves back downwardly through the drill stringto the subsurface signal-receiving station.

A further important aspect of the invention is concerned with the actualgeneration of the torsional acoustic waves within the drill string.According tothis aspect, the invention contemplates two differentmethods of acoustic wave generation. One method involves utilization ofthe torsional acoustic waves which are inherently produced in a rotatingdrill string during a drilling operation. ln this regard, it iswell-known that a drill string cutting bit, in the process of cuttinginto an earth formation, generates large quantities of noise which aretransmitted along the drill string. Since the cutting motion isprimarily a turning or twisting motion, a large component of this noiseis torsional in character, i.e., consists of torsional acoustic waves.Such torsional waves are composed of relatively broadband components andnarrow spectral lines or frequency bands generated by the teeth of acutting bit and the gears in the mechanical drill string drive. Therotation generated torsional waves can be modulated at the bottom of thedrill string in a manner to effectively transmit upwardly through thestrin g selected torsional wave components representing informationsignals. These signals may be detected at the surface to recover thetransmitted information.

The preferred method of acoustic wave generation contemplated by theinvention involves the use of a transducer, preferably a crossed-fieldmagneto-strictive transducer, energized by an electrical driving signalof the proper frequencies to drive the drill string in torsionalacoustic oscillation in a manner to produce in the string torsionalacoustic waves of zero order.

In this latter regard, a further important aspect of the invention isconcerned with a novel crossed-field magnetostrictive transducer for thepresent drill string communication system. This transducer may beutilized as a torsional acoustic wave generator for the drill string, anacoustic signal transmitter, and/or an acoustic signal receiver. A majoradvantage of the transducer resides in its self-supporting constructionwhich permits the transducer to form a load bearing part of the drillstring. One transducer disclosed herein, for example, is embodieddirectly in the drilling kelly. Another advantage of the transducerresides in its ability to drive the drill string in its base band oftorsional acoustic transmission. In this band, the acoustic attenuationor acoustic transmission losses produced by the drill string areminimized. This reduction of the acoustic transmission losses in thedrill string, along with the earlier mentioned reduction in transmissionlosses resulting from the use of torsional waves, enable operation ofthe present communication system in its preferred operating manner,referred to earlier. It will be recalled that in this preferredoperating manner, the torsional acoustic waves are launched downwardlythrough the drill string from the surface, modulated at the subsurfacesignaltransmitting station with the telemetric signals to be monitored,and then returned back to the surface signal-receiving station.

Additional aspects of the invention are concerned with a novel swivelfor the drill string communication system and with the means formodulating torsional acoustic waves in the drill string with the signalsto be transmitted. These modulating means may vary widely in design andconstruction and may be electrical, electronic, or mechanical incharacter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates well bore drillingapparatus embodying a drill string communication system according to theinvention;

FIG. 2 is an enlarged detail of the rotary table kelly and hoist of thedrilling apparatus;

FIG. 3 is an enlarged longitudinal section through the drilling kellyillustrating a magnetostrictive transducer embodied in the kelly;

FIG. 4 is a further enlarged section taken on line 44 in FIG. 3;

FIG. 5 is an enlarged section taken on line 5-5 in FIG. 4;

FIG. 6 is an enlarged section taken on line 66 in FIG. 3;

FIG. 7 is an enlarged section through an inertial modulator embodied inthe communication system;

FIG. 8 is a section taken on line 88 in FIG. 7;

FIG. 9 is a section taken on line 9-9 in FIG. 7;

FIG. 10 is a diagrammatic illustration of the drill string communicationsystem;

FIGS. 11-13 are diagrams of the well bore modulator electronics of thecommunication system;

FIG. 13A is a diagram of the accoustic transmission characteristics of adrill string;

FIG. 14 is a diagram of the top side transducer electronics of thecommunication system;

FIG. 15 is a diagram of the top side transducer electronics of amodified drill string communication system having separate acoustic wavelaunching and receiving transducers;

FIG. 16 illustrates a modified crossed-field magnetostrictive transduceraccording to the invention;

FIG. 17 is a section taken on line 17-17 in FIG. 16;

FIG. 18 is a section taken on line 18Il8 in FIG. 16;

FIG. 19 diagrammatically illustrates a modified drill stringcommunication system according to the invention, wherein modulatedtorsional acoustic waves are launched upwardly from the lower end of thedrill string;

FIG. 20 is a diagram of the surface receiving electronics of thecommunication system of FIG. 19;

FIG. 21 diagrammatically illustrates a further modified drill stringcommunication system according to the invention wherein information istransmitted to the surface only in response to command signals from thesur face;

FIG. 22 illustrates a further modified crossed-field magnetostrictivetransducer according to the invention;

FIG. 23 is an enlarged section taken on line 2323 in FIG. 22 with thefield coil omitted for clarity; and

FIG. 24 illustrates a further modified magnetostrictive transduceraccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to FIGS. 1-14,there is illustrated a communication system 10 according to theinvention for transmitting information through a subsurface pipe 12 froma signal-transmitting station 14 to a signalreceiving station 16 throughan intervening length 17 of the pipe which is capable of sustainingtorsional acoustic oscillations. The communication system includes wavegenerating means 18 for inducing in the pipe 12 torsional acousticwaves, means 20 at the signal-transmitting station 14 for modulatingwaves with a modulating signal representing the information to betransmitted, and receiving means 24 at the signalreceiving station 16for demodulating the modulated waves to recover the transmitted signals.The particular embodiment of the invention selected for illustrationrepresents the primary application of the communication system. In thiscase, the pipe 12 is a drill string suspended within a well bore 26 froma surface drilling platform 28. The communication system is utilized totransmit signals along the drill string between the transmitting andreceiving stations. These transmitted signals may be either controlsignals for operating, from the drilling platform, a device within thewell bore, or telemetric signals representing selected drillingparameters to be monitored at the platform.

The drilling platform 28 is conventional and hence need not be describedin elaborate detail. Suffice it to say that the platform has a derrick30 mounted on a floor 32 and supporting a hoist 34. Hoist 34 includes atraveling block 36 supported by a cable 38 and carrying a swivel 40.This swivel provides a rotatable connection between the traveling blockand the drilling kelly 42 at the upper end of the drill string 12. Kelly42 extends downwardly through a rotary table 44 on the derrick floor 32and through the well casing 46 and a blow-out preventer 48 sealed to thewall of the well bore as at 49. The upper end of the drill string 12proper is connected to the lower end of the kelly. The hoist 34 androtary table 44 are powered by a draw works 50. A drilling fluidcirculation pump 52 delivers drilling fluid or mud under pressure from amud pit S4 or other fluid reservoir to the swivel 40 through a mud hose56. The mud flows downwardly through the kelly 42 and the drill string12 and finally returns to the surface through the well bore, about theoutside of the drill string, and then through blow-out preventer 48. Themud flows from the blow-out preventer back to the reservoir through areturn line 58.

Drill string 12 is composed of individual drill pipe sections 60 ofusually uniform length joined end to end by couplings 62 which arecommonly referred to as tool joints. In some cases the drill string maycontain additional sections, known as drill collars. Each drill stringsection 60 normally has a length of approximately 30 feet. Drill collar63 and a drill bit or cutter 64 are coupled to the lower end of thedrill string.

In operation of the illustrated drilling rig, the rotary table 44 isdriven in rotation by the draw works 50 to drive the kelly 42 and hencethe drill string 12, in its rotary drilling motion. The hoist 34 isoperated to support a portion of the drill string weight, such as tomaintain the proper drilling pressure on the cutter 64. The mud pump 52is operated to provide continuous circulation of drilling mud throughthe well bore to lubricate the cutter and remove debris from the wellbore.

The particular acoustic communication system of the invention which hasbeen selected for illustration in FIGS. 1-l4 is designed for monitoringselected drilling parameters in the vicinity of the drill bit in orderto provide the drilling operator with sufficient information toeffectively control the drilling operation. As noted earlier, typicaldrilling parameters which provide valuable information to the drillingoperator are temperature, formation pressure, formation porosity, drillstring orientation, and others. In this case, the signal transmittingstation 14 is located at the lower end of the drill string 12, and thesignal-receiving station 16 is located at the drilling platform 28.Sensors 65 are shown mounted within the drill collar 63 to sense thedrilling parameters to be monitored. These sensors are connected to themodulating means 20 and provide signals representing the monitoreddrilling parameters. The modulating means processes the sensor outputsignals to provide a modulating or telemetric signal containinginformation representing all of the monitored drilling parameters andmodulates the acoustic waves induced in the drill string 12 by the wavegenerating means 18 with the telemetric signal. The modulated wavestravel up the string to the surface signal-receiving station 16 wherethe waves are demodulated by the receiving means 24 to recover thetransmitted drilling parameter information.

In certain of its aspects the invention contemplates the use of anyacoustic waves capable of modulation by the telemetric signal to betransmitted and capable of propagation through the drill string 12 withsufficiently small acoustic loss and dispersion over the length of thedrill string to provide efficient signal reception at the signalreceiving station 16. In this regard, it is significant to recall thattorsional acoustic waves, however are superior to all other acousticwave forms, such as longitudinal and flexural for acoustic signaltransmission through a drill string, since torsional waves couple lessacoustic energy into the drilling fluid and the wall of the well bore.According to the preferred practice of the invention, especially fordepths at which communication becomes difficult, or otherwiseimpossible, the torsional waves used for signal transmission aretorsional acoustic waves of zero order. Such waves are characterized bypure rotation of each transverse section of the drill string within anadvancing wave front about the longitudinal axis of the string. Themajor advantage of such zero order torsional waves resides in the factthat they are non-dispersive. Most other acoustic modes of propagationare dispersive. Non-dispersive torsional wave propagation is desirable,and essential to rapid efficient signal transmission through a drillstring, since dispersion smears the transmitted signal along the stringand renders difi'icult recovery of the signal at the signal receivingstation.

The frequency of the torsional waves is also an important factor inefficient signal transmission through the drill string 12 in that thecouplings 62 which join the drill string pipe sections acoustically loadthe string and the mud about the string attenuates higher frequencies ofacoustic oscillation. The jointed string thus tends to pass loweracoustic frequencies with less attenuation than higher frequencies, dueto the frequency dependent attenuation of the mud, while the couplings62 introduce Zeros of transmission as shown in FIG. 13A. According tothe preferred practice of the invention, the frequency of the torsionalacoustic waves employed for signal transmission is selected to effectwave propagation through the drill string in its base band oftransmission. This is the band from zero frequency to the first zero oftransmission P In this band, the mud produces minimum attenuation of thewaves and thus permits maximum signal transmission through the string.However, in its broader scope, the invention contemplates acoustic wavepropagation through the drill string in its higher pass bands so long assuitable signal reception is possible at the signal receiving station.As will appear from the later description, operation of the presentdrill string communication system in the base band is permitted by aunique crossed-field magnetostrictive transducer of the inventioncapable of inducing in the string torsional acoustic waves of therelatively low frequency required for such base band operation.

In its broader aspects, the invention also contemplates various means 18for inducing or launching the torsional acoustic waves through the drillstring 12. The preferred torsional wave launching means is a torsionalacoustic wave generator including a crossed-field magnetostrictivetransducer. An important feature of the invention in this regard residesin novel crossed-field magnetostrictive transducer configurations whichmay be utilized to launch the waves through the drill string as well asto modulate the waves and receive the modulated waves. A unique featureof these transducers is their rugged self-supporting construction whichpermits the transducers to form an integral load supporting element ofthe rotating drill string system. The drill string communication systemin FIGS. 1-14, for example, employs a crossed-field magnetostrictivetransducer which is embodied in and forms a load bearing part of thekelly 42. An alternative method of acoustic wave generation contemplatedby the invention involves utilization of the torsional acoustic waves ortorsional noise inherently produced in a rotating drill string.

The earlier discussed reduction in acoustic transmission lossesresulting from utilization, in the present drill string communicationsystem, of torsional acoustic waves, particularly zero order torsionalwaves within the base band frequency range of the drill string 12,together with the self-supporting construction of the presentmagnetostrictive transducers permits various types of acoustic wavecommunication through the drill string. When monitoring drillingparameters, such as those mentioned earlier, the preferred method ofcommunication involves launching the waves downwardly through the drillstring from the surface to the subsurface signal-transmitting station14. The waves are modulated at this station with the telemetric signalrepresenting the drilling parameters to be monitored and returnedupwardly through the drill string to the surface signal receivingstation 16. A primary advantage of this communication method resides inthe fact that the torsional wave generating transducer may be locatedout of the well bore. The transducer is then isolated from the hostileenvironment in the well bore, is readily accessible for servicing andrepair without removal of the drill string, and is free of the designconstraints imposed by the drill string envelope.

The drill string communication system illustrated in FIGS. l-l4 employsthis preferred method of acoustic communication. Referring now ingreater detail to this communication system, the means 18 for inducingtorsional acoustic waves in the drill string 12 comprises a torsionalacoustic wave generator which is embodied in the drilling kelly 42.Broadly, these may be of any suit able form. The preferred generator,however, includes a lower crossed-field magnetostrictive transducer 66according to the invention, and an upper torque reaction stub 70, asshown in FIG. 3. The transducer and torque reaction stub have tubularbodies 72, 76, respectively, rigidly joined end to end in any convenientway. These tubular bodies have a uniform, noncircular, usually square,cross section matching that of a conventional drilling kelly andtogether constitute the drilling kelly 42.

The lower end of the kelly 42, that is, the lower end of transducer body72, is coupled to the upper end of the drill string 12 by a tool joint78. Swivel is rotatably coupled to an extension 79 at the upper end ofthe kelly, that is, to the upper end of the upper reaction stub body 76.As shown in FIGS. l-l4, this swivel has an inverted cup-like housing 80receiving the upper end of the stub body extension 79. The housing isattached to the extension by a pair of combined radial and thrustbearings 82. A seal ring 84 provides a liquid tight seal between thehousing and extension. The kelly 42 is thus restrained againstlongitudinal movement but is free to rotate relative to the swivelhousing 80. At the upper end of the housing is a lifting bail 86 bywhich the housing and hence the kelly 42 and drill string 12, aresuspended from the travelling block 36 of hoist 34.

The mud hose 56 connects to the swivel housing 80 and opens to theinterior housing chamber 88 above the seal 84. Extending centrallythrough the kelly 42 is a mud passage 90 through which drilling mudentering the chamber 88 through the mud hose 56 flows to the central mudpassage in the drill string 12.

As noted above, the torsional wave transducer 66 is a crossed-fieldmagnetostrictive transducer. Transduc ers of this general class areknown in the art. Such a transducer requires an elongated body ofmagnetostrictive material and means for establishing two magnetic fieldswithin the body. One field is an axial field whose field lines extendlongitudinally through the body. The other field is a transverse fieldwhose field lines extend circumferentially through the body. One fieldis commonly referred to as a bias field and the other as a signal field.Either field may serve as the bias field and the other field as thesignal field. The interaction of the bias and signal fields produces atorsional strain in the body which may be caused to fluctuate in such away as to induce torsional oscillations in the body by varying, at theproper frequency, either or both the bias and signal fields. In thismode, the transducer is either a torsional wave generator or modulator,i.e., signal transmitter. The transducer is also capable of operating inan acoustic signal receiving mode. Thus, a torsional strain within thetransducer body with only one of the transducer fields present inducesin the other field conductors a voltage, at the conductor terminals,proportional to the rate of strain. The communication system of FIGS.l-14 employs the magnetostrictive transducer 66 as both a torsional wavegenerator and a signal receiver.

In such a crossed-field magnetostrictive transducer, the fields in thelongitudinal and circumferential directions may be established invarious ways. For example, the field in the circumferential directionmay be established by passing a current longitudinally through thetransducer body or through a conductor within the body. The field in thelongitudinal direction may be established by passing a current through acoil surrounding the body. Alternatively, either field may beestablished by constructing the transducer body ofa magneticallyremanent magnetostrictive material which is permanently magnetized inthe proper direction. The field in the longitudinal direction may alsobe established by permanent magnets along the transducer.

Suitable materials for the body of a transducer designed for suchremanent operation are iron cobalt alloys, such 3850-50 iron cobalt, orternary iron cobalt alloys, such as 2V Permandure containing approxi'mately 49 percent iron, 49 percent cobalt and 2 percent vanadium, ornickel-cobalt alloys such as Ni204 containing approximately 4 percentcobalt and 96 percent nickel. Also suitable are iron-nickel-cobaltalloys, including multi-element alloys based on the ironnickel-cobaltcomplex as are many alloys consisting of one of the magnetic elementsiron-nickel-cobalt in combination with non-magnetic elements such as analloy consisting of approximately 12 percent aluminum and 88 percentiron. For non-remanent transducer operation, the transducer body may beconstructed of nickel or any of the magnetostrictive alloys of nickeland iron commonly called p ermalloys, such as 50- 50 nickel iron, orsome of the more complex alloys such as NiSpan C, containing nickel,iron, titanium, and chromium.

It is significant to note here that in the present drill stringcommunication applications, the mechanical properties of the transducerbody also enter into the selection of the magnetostrictive material forthe body. Foremost among these mechanical properties are machinability,tensile strength, effect of tensile stress on the magnetostrictivecharacteristics, electrical conductivity, and others.

The crossed-field magnetostrictive transducer 66 embodied in the welldrilling apparatus of FIGS. 1l4 is designed for remanent operation. Tothis end the transducer body 72 has a major central portion 72Pconstructed of a magnetically remanent magnetostrictive material. Inthis instance the material is biased with a remanent field in thelongitudinal direction.

Fixed to and extending the full length of the kelly mud passage 90 is asleeve 94 of copper or the like which provides an inner signal-fieldconductor of the transducer. Fixed within channels 96 in the four sidesof and extending the full length of the kelly 42 are strips 98 of copperor the like which provide outer signalfield conductors of thetransducer. These outer conductors are electrically insulated from thetransducer body 72 by electrical insulation 100. The lower ends of theinner and outer conductors 94, 98 are electrically connected at 102. Theupper ends of the conductors are electrically connected to the leads ofa cable 104 through collector rings 106 surrounding the upper endof thekelly 42 and collector brushes 108 carried by the swivel housing 80. Theupper collector ring is assured good electrical contact to the innerconductor by means of copper rivets 107. The lower collector ring is indirect electrical contact with the outer conductors.

As will be explained in more detail presently, a driving signal isapplied to the transducer signal-field conductors 94, 98, through thecable 104. This driving signal produces in the conductors a fluctuatingcurrent which induces in the transducer body 72? a circumferentialmagnetic signal field that interacts with the longitudinal remanent biasfield of the body to produce an alternating torsional strain in thebody. Such alternating torsional strain, in turn, propagates as atorsional wave downwardly through the drill string 12 to the subsurfacesignal transmitting station 14. The torsional waves are modulated at thesignal transmitting station with a telemetric signal representing thedrilling parameters to be monitored and returned upwardly through thedrill string to the surface, in the manner to be explained presently.These modulated waves are received by the transducer 66 and thendemodulated to recover the transmitted signal.

It will be recalled from the earlier description that the invention, inits broader aspects, contemplates any torsional acoustic waves capableof propagation through the drill string 12 and capable of modulation bythe telemetric signal to be monitored to achieve effective signaltransmission from the subsurface signal transmitting station 14 to thesurface signal receiving station 16.

It will be further recalled, however, that the preferred waves aretorsional acoustic waves of zero order and of the proper frequency toeffect wave propagation through the drill string 12 in its base band. Inthis latter regard, attention is directed to FIG. 13A. This figuredepicts the relationship between quantity T, representing the relativetransmission of torsional acoustic wave propagation through a drillstring, and the frequency f of the torsional waves expressed in units ofthe quantity f,,. This latter quantity is the torsional wave frequencyat which the transmission quantity T first becomes zero. The frequencyquantity f, is related to the velocity of torsional wave propagationthrough the drill string and a distance d, (the effective acousticdistance between the drill string couplings 62) by the followingequation.

As indicated in FIG. 13A, the base band of torsional wave propationthrough the drill string 12 occurs in the region between f 0 and f f,,.From this it will be understood that propagation of the torsionalacoustic waves of the invention through the drill string 12 isaccomplished by exciting the transducer 66 with a driving signal havingfrequency components such that if f is the frequency of a component,then f/fo l For a standard drill string composed of 30 foot pipesections and conventional tool joint couplings 62, f, is on the order of80 Hz.

Returning again to the torsional wave transducer 66, the transducer body72 will be recalled to have a torque reaction stub which provides anacoustic reaction termination at the upper end of the transducer. Whilethis upper reaction stub or termination may conceivably be designed toserve as an absorbing termination, the particular termination shown isassumed to be a refleeting termination.

The theory of reflecting terminations is well understood and hence neednot be explained in great detail. Suffice it to say that the correctlength of a reflecting termination depends on the nature of thereflections occurring at the upper end of the termination. For ex ample,if the upper end of the termination is open or free, with no acousticconnection to any structure, the end constitutes a node for torque andan antinode for torsional displacement. In this case, the optimumtermination length is an odd number. of quarter wave lengths of theacoustic waves to be reflected. On the other hand, if the end of thetermination is acoustically rigid, that is, anchored to a very largemass with an acoustic impedance large relative to that of the transducerand termination, the end of the termination is an antinode for torqueand a node for torsional displacement. In this case, the optimumtermination length is an even number of quarter wave lengths of theacoustic waves to be reflected. For intermediate cases, the terminationmust have an intermediate length determined by the acoustic conditionsat the end of the termination. Obviously, the torque reaction stub ortermination 70 represents such an intermediate case and must bedimensioned accordingly.

It will be understood from the description to this point that thetransducer 66 is excited with a driving signal of the proper frequenciesto launch torsional acoustic waves of zero order downwardly through thedrill string 12 in the base band of the drill string. The manner inwhich this driving signal is generated will be explained presently.Suffice it to say here that the driving signal is applied to thetransducer through the cable 104, collector brushes 108, collector rings106 and the upper rivets 107. The waves are modulated at the subsurfacesignal transmitting station 14 by the modulating means 20 and returnedto the signal receiving station 14, to provide at the receiving stationmodulated waves containing information representing the drillingparameters to be monitored.

It will be immediately evident to those versed in the art that a varietyof acoustic wave modulating means 20 may be employed in the presentdrill string communication system. FIGS. 7-9 illustrate an inertialmodulator for the system. This inertial modulator has a central tube orpipe 110. Surrounding the upper end of the modulator pipe 110 is arelatively massive inertial cylinder 118. Inertial cylinder 118 isrotatably supported on and restrained against movement along the pipe110 by combined radial and thrust bearings 120. Seals 122 seal the endsof cylinder to the pipe. Between its ends, the inertial cylinder 118 isinternally enlarged to define an annular chamber 124 between thecylinder and the pipe 110. This chamber is filled with a magnetic fluid126, such as a mixture of oil and powdered iron. Contained in fouruniformly spaced longitudinal slots 128 in the portion of the modulatorpipe 110 within the chamber 124 is a drive coil 130. As shown best inFIG. 8, the conductors of the drive coil extend lengthwise of the slots128. Moreover, as indicated by the and signs in the figure, the drivecoil is wound in such a way that when a voltage is impressed across thecoil, current flows in one direction through the conductors in twodiametrically opposed slots and in the opposite direction through theconductors in the remaining two diametrically opposed slots.

It will now be understood that the modulator structure described thusfar constitutes, in effect, an electromagnetic clutch. Thus, when thedrive coil 130 is deenergized, the pipe 110 and inertial cylinder 118are capable of relatively free relative rotation. Energizing of thedrive coil produces a magnetic coupling between the pipe and cylinderwhich resists relative rotation of the pipe and cylinder with a torqueproportional to the current flow through the drive coil.

Surrounding and fixed to the modulator pipe 110 below the inertialcylinder 118 is an annular circuit housing 132 containing the drivingcircuit 134 for the modulator drive coil 130. The drive coil isconnected to the output of the circuit through leads 135. Modulatordriving circuit 134 will be described shortly.

Between the modulator and the drill collar 63 is a lower reactancetermination 136. This reactance termination comprises a section of drillpipe or a pipe collar of the proper mass and length to constitute areflecting termination for the torsional accoustic waves launcheddownwardly through the drill string 12 by the topside transducer 66. Theearlier discussion relative to the topside reflecting termination 70applies with equal force to the termination 136. The modulator pipe 110and lower termination are connected end to end in the drill string 12 byconventional tool joints. In this regard, it will be observed that thelatter pipe and termination transmit drilling torque to the drillingcutter 64 and support the weight of the drill string below and thus mustbe designed to have sufficient torsional and tensile strength towithstand these loads. Extending through the pipes are mud passageswhich form a continuation of the drill string mud passage.

As noted earlier, it is desirable or necessary during a drillingoperation to monitor several different drilling parameters in thevicinity of the drilling cutter 64. Some of these parameters were listedin the earlier description and thus need not be repeated here. Sufficeit to say that the sensors 65 are selected and arranged within the drillcollar 63 to be responsive to the particular drilling parameters to bemonitored. In this regard, it is significant to note that sensors forthis purpose are well-known and available on the commercial market.Accordingly, it is unnecessary to describe the sensors except to saythat each sensor produces an electrical output representing itsrespective drilling parameter.

The several sensors 65 are electrically connected through leads 146 tothe input of the modulator driving circuit 134.

The modulator driving circuit 134 will be explained presently. Sufficeit to say here that the circuit effectively combines the several outputsfrom the drilling parameter sensors 65 and produces a telemetric signalcontaining information representing all the drilling parameters. Thistelemetric signal is processed to produce a corresponding modulatordriving signal which is applied to the modulator drive coil 130 andproduces a corresponding fluctuating magnetic coupling between the innerpipe 1 l0 and outer inertial cylinder 1 18 of the modulator 20. As aconsequence the torsional acoustic waves propagating downwardly throughthe drill string 12 and the modulator pipe to the lower reactiontermination 136 and then reflected from the termination upwardly throughthe pipe and drill string are modulated to contain informationrepresenting the drilling parameters being monitored. Thus, an increasein the magnitude of the modulator driving signal produces acorresponding increase in the magnetic coupling between the modulatorpipe and inertial cylinder, thereby increasing the effective torsionalmass of the pipe and retarding the phase as well as altering theamplitude of the waves when traveling through the modulator. Similarly,a decrease in the magnitude of the driving signal produces acorresponding reduction in the magnetic coupling between the modulatorpipe and intertial cylinder, thereby reducing the effective torsionalmass or movement of the pipe and advancing the phase as well as alteringthe amplitude of the waves then traveling through the modulator.

The modulated waves travel upwardly through the drill string 12 to thesurface signal receiving station 16. These modulated waves produce acorresponding fluctuatingtorsional strain in the magnetostrictive body72 of the transducer 66, thereby inducing in the transducer fieldconductors 94, 98 a fluctuating voltage containing informationrepresenting the transmitted telemetric signal. As explained below, thevoltage signal from the transducer is processed by a combined transducerdriving-receiving circuit at the surface to recover the transmittedinformation representing the drilling parameters being monitored.

A variety of torsional acoustic modulators, other than the inertialmodulator described above may be employed in the present drill stringacoustic communication system. By way of example, a crossed-fieldmagnetostrictive transducer sirnilar to the top side transducer 66 maybe employed as a modulator. In this regard, attention is directed toFIGS. 16-18 illustrating a modified magnetostrictive transducer 66baccording to the invention which may be utilized as a modulator. Thissame transducer configuration may be utilized to launch modulatedtorsional acoustic waves through the drill string, as will be describedin connection with the communication system of FIGS. 19 and 20.

Turning now to FIG. 11 there is illustrated the general arrangement ofthe modulator driving circuit 134 which is contained in the modulatorcircuit housing 132. As noted, this circuit converts the outputs fromthe drilling parameter sensors 65 to a coded driving signal for themodulator 20. This driving circuit includes a power source (not shown),such as a battery, an encoder 148 and modulator driving circuitry 150.The encoder is connected to the drilling parameter sensors 65 to receivethe several sensor outputs and processes these outputs to produce atelemetric signal containing information representing all of the sensoroutputs. This telemetric signal is applied to the driving electronics150 which processes the signal in such a way as to produce a modulateddriving signal for the modulator drive coil 130.

The driving circuit 134 may utilize various signal processing techniquesfor converting the outputs from the drilling parameter sensors 65 to asuitable driving signal for the inertial modulator or for acrossed-field magnetostrictive transducer when employed as a modulator.FIGS. 12 and 13 illustrate possible signal processing techniques forthis purpose. These illustrated signal processing techniques arewell-known and understood so that an elaborate description of the sameis unnecessary.

Suffice it to say that FIG. 12 is a binary phase coded system whereinthe encoder 148 is a binary digital encoder for converting the analogoutputs from the sensors 65 to a binary digital signal containinginformation representing the outputs of all the sensors. the modulatordriving circuit 150 is a power amplifier which amplifies this binarydigital signal to the proper strength for driving the modulator 20. FIG.13 is a frequency shift keyed system suitable for use with amagnetrostrictive transducer as will be explained presently inconnection with communication system 10b (FIGS. 19 and 20). In thiscase, the encoder 148 is a digital encoder which converts the outputs ofthe sensors 65 to a digital frequency shift keying signal containinginformation representing all of the sensor outputs. The modulatordriving electronics 150 includes a frequency shift keyer 1500 whichconverts the encoder output to a frequency shifted transducer drivingsignal and a power amplifier 15017 for amplifying the signal to theproper strength for driving the transducer.

Considering now the system of FIG. 10, there is connected to the topsidetransducer 66 a driving and receiving electronic system 152, comprisingmeans 154 (FIG. 14) for separating the driving signal to and theinformation signal from the transducer. The means 154 shown in FIG. 14is a hybrid junction having one branch connected to the transducer fieldconductors 94, 98. A second branch of the hybrid is connected to atransducer driving circuit 156 including a high power drive source 158.Connected to the third branch of the hybrid is a transducer receivingcircuit 160 including an amplifier 162, phase detector 164, digitaldecoder 166, and an output display or recorder 168. The reference inputof the phase detector 164 is connected to the source 158 through anattenuator 170.

The operation of transducer 66 and driving and receiving circuit 152will be immediately evident to those versed in the art. Thus, the hybridjunction 154 feeds the high power driving signal from the source 158 tothe transducer field conductors 94, 98 to drive the transducer to launchthe earlier described torsional acoustic waves downwardly through thedrill string 12. At the subsurface signal transmitting station 14, thesewaves are modulated to contain the information representing thetelemetric signal to be transmitted and are returned upwardly throughdrill string 12. These modulated waves produce a fluctuating torsionalstrain in the transducer body 72 and thereby a corresponding fluctuatingvoltage signal in the transducer field conductors 94, 98. The hybridjunction 154 feeds this voltage signal to the receiving circuit 160.This signal is amplified by amplifier 162 and its phase is compared tothe phase of the transducer driving signal in the phase detector 164 toprovide an output representing the telemetric signal. The digitaldecoder 166 reduces the output of the phase detector to discrete outputsignals representing the various monitored drilling parameters. Theseoutput signals are then displayed or recorded as drilling parameterinformation by the display or recorder 168.

In some applications it may be desirable or essential to employ separatetransducers at the surface for launching the torsional acoustic wavesdownwardly through the drill string 12 to the subsurface signaltransmitting station 14 and receiving the modulated waves returning tothe surface. FIG. 15 illustrates such a dual transducer communicationsystem 10a. In this system, the single transducer 66 in FIGS. l-14 isreplaced by launch and receive transducers 66L, 66R coupled end to endat the upper end of the drill string. The launch transducer has adriving circuit 170 comprising a low power source 172 connected througha power amplifier 174 to the field conductors 94, 98 of the transducer.The receiving transducer has a receiving circuit 176 connected to thefield conductors 94, 98 of the transducer. This circuit includes ablanking circuit 178, phase detector 180, digital decoder 182, andoutput display or recorder 184. A pulse keyer 186 is connected to theamplifier 174 and blanking circuit 178, phase detector 180 is connectedthrough an attenuator 188 to the source 172.

The operation of communication system 10a is similar to that ofcommunication system 10, except that the driving and receiving circuits170, 176 are activated alternatively by the pulse keyer 186. During theintermittent transducer driving modes of the system 10a, the pulse keyerconditions the launch amplifier 174 to feed an amplified signal to thelaunch transducer 66L and conditions the blanking circuit 178 to blockthe output of the receiver transducer 66R. Under these conditions thelaunch transducer 66L is driven by the amplified driving signal from thesource 172 to launch torsional acoustic waves downwardly through thedrill string 12. During the intervening transducer receiving modes ofthe system, the pulse keyer 186 conditions the launch amplifier 174 toblock signal transmission to the launch transducer 66L and conditionsthe blanking circuit 178 to pass the output of the receiver transducer66R Under these conditions, the fluctuation voltage signal induced inthe receiving transducer 66R by the returning modulated waves is fed tothe receiving circuit 176 to produce a display or recording of thedrilling parameter information being monitored.

The present drill string communication systems described to this pointemploy the preferred mode of wave propagation from the surface to thesubsurface signal transmitting station and return of the modulatedacoustic waves to the surface. The reasons why this mode of propagationcan be employed and its advantages were explained earlier and need notbe repeated here. In some applications, it may be desirable or necessaryto employ the alternate mode of wave propagation referred to earlier,i.e., launching of the modulated waves directly from the subsurfacesignal transmitting station 14. FIGS. 19 and 20 diagrammaticallyillustrate a drill string communication system 10b which employs thisalternate propagation mode.

Communication system b is identical to system 10 except for thereplacement of the modulator by the crossed-field magnetostrictivetransducer 66b of FIGS. 16-18 and modification of the transducer drivingand receiving electronics. Turning first to FIGS. 16-18, it will be seenthat the subsurface transducer 66b is similar to the topside transducer66 and differs from the latter in that transducer 66b is inverted andincludes a circuit housing 190 surrounding the lower end of thetransducer body 72. Within this housing is the electronic circuitry 192for processing the outputs of the drilling parameter sensors 65 toproduce a modulated transducer driving signal containing informationrepresenting the drilling parameters being monitored. Also the outertransducer field conductor 98 is a copper sleeve, rather than barsfitting in slots in the tranducer body as in the topside transducer 66.Transducer 66b may employ such an outer conductor sleeve, of course,since it is not required to couple to the driving torque of the rotarytable 44, as with the topside transducer.

During operation of the drill string communication system 10b of FIGS.19, 20, the lower well bore transducer 66b is driven by the modulateddriving signal from its driving circuitry 192 to launch upwardly throughthe drill string 12 modulated torsional acoustic waves containinginformation representing the drilling parameters being monitored. Thesemodulated waves induce in the field conductors 94, 98 of the topsidetransducer 66 a fluctuating voltage which is processed to recover thedrilling parameter information.

The driving electronics 192 for the lower well bore transducer 66b mayembody circuitry similar to that of FIG. 13, described earlier, forconverting the output signals from the drilling parameter sensors 65 toa modulated transducer driving signal. In the case of transducer 66b,however, it will be understood that the driving electronics will includea power source capable of producing the energy required to induce in thedrill string the desired acoustic torsional waves. Such a power sourcemay comprise a battery connected to a charging generator driven by mudflow through the drill string. FIG. 20 illustrates the receiving circuit198 for the topside transducer 66. The operation of this receivingcircuit will be obvious to those versed in the frequency shift keyingsystems.

At this point, it is significant to recall that the well bore transducer66b of FIGS. 16-18 may be employed as a modulator in a communicationsystem which utilizes the preferred mode of wave propagation discussedin connection with FIGS. 1-14. In this regard, it will be understoodthat the communication system 10b of FIGS. 19, 20 may be operated inthis preferred propagation mode by utilizing the well bore transducer66b as a modulator only and replacing the topside receiving circuit 198with a combined transducer drivingreceiving circuit such as shown at 152of FIGS. 10 and 14 for operating the topside transducer 66 to launchtorsional waves downwardly through the drill string and receive thereturning modulated waves.

The communication systems described to this point are designed primarilyfor relatively continuous monitoring of selected drilling parameters. Itshould be noted in this regard that in some drilling applications it maybe possible to communicate effectively through the drill string 12 whiledrilling is actually in progress, i.e., while the string is being drivenby the rotary table 44. In other cases, effective communication mayrequire cessation of the drilling operation and release of the rotarytable gripping jaws from the drill string.

FIG. 21 diagrammatically illustrates a drill string communication system100 for transmitting drilling parameter information to the surface onlyin response to selected command or interrogation signals from thesurface. The communication system selected for illustration is identicalto that of FIGS. 19, 20 with the exception of the circuitry for thesurface transducer 66 and the well bore transducer 66b. The surfaceelectronic circuitry comprises a combined drivingreceiving circuit 200for the surface transducer 66 including a hybrid junction 202 having onebranch connected to the field conductors of the topside transducer 66. Adriving signal source 204 is connected to a second branch of the hybridthrough a modulator or encoder 206 and a launch amplifier 208. The thirdbranch of the hybrid is connected to a readout display or recorder 210through a receive amplifier 212 and a demodulator or decoder 214. In thedrilling parameter interrogate mode of the communication system 10c, thesurface transducer 66 is driven by the driving signal source 204 tolaunch downwardly through the drill string 12 torsional acoustic wavescontaining the command signals. These command signals actuate the wellbore signal transmitting means, as explained below.

The electronic circuitry for the well bore transducer 66b comprises atransducer driving circuit 215 like that of FIG. 11 and including adigital encoder 216 for transforming the outputs of the drillingparameter sensors into a telemetric signal which is applied to thetransducer 66b through an amplifier 218 and hybrid 220. The well borecircuitry also includes an actuator 222 connected to the transducer 66bthrough an amplifier 224 and the hybrid 220. This actuator is anelectrical switch device connected between the power source 226 for thewell bore circuitry and the driving circuit 215 and is actuated by thecommand or interrogation signals from the source to open and close theenergizing circuit between the driving circuit 215 and power source 226.Actuators of this kind are well-known in the art. Accordingly, it isunnecessary to describe the actuator in detail.

Suffice it to say that in the normal operating mode of the communicationsystem 10c, actuator 222 presents an open circuit between the powersource 226 and the transducer driving circuit 215 so that no drillingparameter information is transmittedto the surface. The transponder isactivated in response to the command signals from the surface to connectthe power source to the driving circuit. Under these conditions, thedriving circuit feeds to the well bore transducer a coded telemetricsignal representing the outputs of sensors 65 for producing in the drillstring 12 modulated acoustic waves which propagate to the surface wherethe waves are received and demodulated and their contained informationis displayed or recorded by the receiving circuit 210, 212, 214. Themajor advantage of such a communication system is the conservation ofthe energy required to operate the well bore signal transmission systemduring those periods when transmission of information is not required.Obviously a similar arrangement may be employed to operate other devicesin the well bore on command.

FIGS. 22, 23 illustrate a modified crossed-field magnetostrictivetransducer 300 which may be employed in the invention. In thistransducer, the longitudinal field is established by current flowthrough a coil 302 about the transducer body 304 rather than by magneticremanence in the body. The circumferential field is established bycurrent flow through longitudinal conductors 305 on the body.Alternatively, the circumferential field may be established by the useof a remanent transducer body which has a permanent field in thecircumferential direction. As noted earlier, either the longitudinalfield or the circumferential field of the transducer may be employed asthe bias field and the remaining field as the signal field, or bothfields may be used as signal fields. The transducer of FIG. 24 is likethat of FIGS. 22, 23, except that the longitudinal field is estab lishedby permanent magnets 307.

In relatively large transducers, such as are required for the presentdrill string communication applications, however, the inductance of thelongitudinal field coil 302 and the corresponding time constant of thecoil circuit may be so large that the frequency response of thetransducer may be too low. In this case, it is necessary to use thelongitudinal field of the coil as a bias field and the circumferentialfield of the longitudinal transducer conductors as the signal field.Moreover, when the longitudinal field of the coil 302 is employed as thesignal field, the transducer body 304 must be longitudinally slotted at306 to prevent the signal field from inducing circumferential eddycurrents in the body. When used in a drill string communication system,the body slot is sealed against mud leakage in any convenient way. Thisslot preferably extends only the length of the central magnetostrictiveportion of the body to preserve the strength of its joints. In thiscase, high reluctance buffer sections 308 may be placed between theslotted body portion and tool joints to permit the longitudinal field toleak out to prevent eddy currents in the drill string and torquereaction stub. These buffer sections may be longitudinally slotted forthe same reason as the body. When the circumferential field is employedas the signal field, the body slot is not required since the eddycircuits flow lengthwise of the transducer body and become negligibledue to the long path length through the body.

The discussion to this point has been concerned with transduceroperation only in a mode wherein the bias field is constant and thesignal field is varied to launch torsional acoustic waves through thedrill string 12 and modulate acoustic waves with drilling parameterinformation. However, the invention contemplates within its scopemodulation of both fields. The transducer then becomes a multiplierwherein the instantaneous torque produced in the transducer body is theproduct of the bias and signal field amplitudes. This multiplieroperating mode is particularly useful when the transducer is used as amodulator.

In the communication systems described to this point, an electricallydriven transducer has been employed to generate the torsional acousticwaves in the drill string. As noted earlier, however, the communicationsystem may utilize as an information carrier the torsional noise oracoustic waves inherently generated in a drill string during a drillingoperation. Such noise consists of relative broad band random noise andnarrow frequency bands both of which may be modulated to transmitinformation through the drill string. The communication system of FIG.19, may be operated in this fashion by using the inertial modulator andeliminating the lower drill string acoustic termination 136. In thisoperation a selected frequency band of the drilling noise is modulatedby the inertial modulator and the topside transducer receiving circuit198 is provided with a filter for passing'only the selected frequencyband. This selected frequency band of the output signal from the surfacetransducer 66 is processed to recover the transmitted information.

Those versed in the art will understand at this point that the drillstring in the varous disclosed inventive embodiments constitutes anacoustic transmission line and that the various elements in the drillstring, such as tool joints, acoustic wave generator and modulator, andthe like, constitute perturbations in the string at which occur acomplex action of partial reflection and partial transmission of theacoustic waves traveling through the drill string. However, it can bedemonstrated by well-known mathematical transmission line analysistechniques that during operation of the present well bore communicationsystem, the several acoustic wave reflections and transmissions resultin transmission from the signal transmitting station to the signalreceiving station of net or resultant modulated acoustic wavescontaining information representing the signal impressed on themodulator or transducer at the transmitting station and hence alsorepresenting the drilling parameter or other information to betransmitted. These net or resultant modulated acoustic waves aredemodulated at the signal receiving station in the manner heretoforeexplained to recover the transmitted information.

From the foregoing description, it will be understood that variouschanges in the detailed construction and arrangement of the partsconstituting the telemetering system for oil wells of the presentinvention may occur to those skilled in the art without departing fromthe spirit and scope of the present invention. Accordingly, it is to beunderstood that the foregoing description is considered to beillustrative of, rather than limitative upon, the invention as definedby the appended claims.

We claim:

1. A method of communicating information between signal-transmitting andsignal-receiving stations spaced along a pipe having an interveninglength between said stations capable of sustaining zero order torsionalacoustic waves, said method comprising the steps of:

generating a modulating signal containing the information to betransmitted;

establishing in said pipe zero order torsional acoustic waves which aremodulated according to a predetermined modulating mode by saidmodulating signal to contain the information to be transmitted and whichtravel from said transmitting station to said receiving station throughsaid intervening pipe length; and

receiving said waves at said receiving station to recover said signaland its contained information.

2. The acoustic communication method according to claim 1 wherein:

said pipe is a drill string suspended from a drilling platform.

3. The communication method according to claim 1 wherein:

said pipe is a drill string suspended within a well bore from a drillingplatform;

at least one of said stations is located within said well bore; and

said torsional acoustic waves are induced in said drill string bydriving said drill string in torsional oscillation at frequencies withina selected range of frequencies. 4. The acoustic communication methodaccording to claim 1 wherein:

said pipe is a drill string suspended within a well bore from a drillingplatform; said transmitting station is located within said well bore andsaid receiving station is located above said transmitting station; andsaid torsional acoustic waves are established in said drill string bydriving said string in torsional oscillation at frequencies within aselected range of acoustic frequencies to launch said acoustic wavesupwardly through said drill string to said receiving station. 5. Theacoustic communication method according to claim 1 wherein:

said pipe is a drill string suspended within a well bore from a drillingplatform; said drill string is composed of a number of pipe sectionscoupled end to end by intervening couplings; and the acousticfrequencies of said torsional acoustic waves are related to the nominallength of said drill string sections in a manner such that said drillstring oscillates in at least one of its pass bands of torsionaloscillation. 6. The acoustic communication method according to claim 5wherein:

the acoustic frequencies of said torsional acoustic waves are related tothe nominal length of said drill string sections in a manner such thatsaid drill string oscillates in its base band of torsional oscillation.7. The acoustic communication method of claim 1 wherein:

said pipe is a drill string suspended within a well bore from a drillingplatform; said receiving station is located within said well bore; saidtransmitting station is located above said receiving station; and saidsignal is a command signal for effecting a selected function at saidreceiving station. 8. The acoustic communication method of claim 1wherein:

said pipe is a drill string suspended within a well bore from a drillingplatform;

said transmitting station is located within said wellbore and saidreceiving station is located above said transmitting station; saidcommunication method comprises the further step of transmitting commandsignals through said drill string to said transmitting station; and saidmodulated acoustic waves are established in said drill string inresponse to said command signals. 9. A communication system forcommunicating information between signal-transmitting andsignalreceiving stations'spaced along a pipe having an interveninglength between said stations capable of sustaining zero order torsionalacoustic waves, said system comprising:

means for generating a modulating signal containing the information tobe transmitted; means for establishing in said pipe zero order torsionalacoustic waves which are modulated by said modulating signal to containthe information to be transmitted and which travel from saidtransmitting station to said receiving station through said interveningpipe length; and receiving means coupled to said pipe at said receivingstation for receiving said modulated waves to recover said signal andits contained information. 10. An acoustic communication systemaccording to claim 9 wherein:

said pipe is a drill string suspended within a well bore from a drillingplatform; and at least one of said stations is located within said wellbore. 11. An acoustic communication system according to claim 10wherein:

said means for establishing said acoustic waves comprises a torsionalwave transducer coupled to said drill string for inducing in said drillstring torsional acoustic waves of zero order. 12. A communicationsystem according to claim 9 wherein:

said pipe is a drill string suspended within a well bore from a drillingplatform; said drill string is composed of a number of pipe sectionscoupled end to end by intervening couplings; and the acousticfrequencies of said torsional acoustic waves are related to the nominallength of said drill string sections in a manner such that said drillstring oscillates in at least one of its pass bands of torsionaloscillation. 13. An acoustic communication system according to claim 11wherein:

said drill string is composed of a number of pipe sections coupled endto end by intervening couplings; and said transducer is adapted to bedriven to produce in said drill string torsional acoustic waves relatedto the nominal length of said drill string sections in a manner suchthat said drill string oscillates in at least one of its pass bands oftorsional oscillation. 14. An acoustic communication system according toclaim 13 wherein:

said drill string is composed of a number of pipe sections coupled endto end by intervening tool joints; and the acoustic frequencies of saidtorsional acoustic waves are related to the nominal length of said drillstring sections in the manner such that said drill string oscillates inits base-band of torsional oscillation. I 15. An acoustic communicationsystem according to claim 9 wherein:

said pipe is a drill string suspended within a well bore from a drillingplatform; said transmitting station is located within said well bore andsaid receiving station is located above said transmitting station; andsaid means for establishing said acoustic waves comprises an electricaltransducer coupled to said drill string and adapted to be energized byan electrical driving signal to launch said acoustic waves upwardlythrough said drill string to said receiving station. 16. An acousticcommunication system according to claim 9 wherein:

1. A method of communicating information between signaltransmitting andsignal-receiving stations spaced along a pipe having an interveninglength between said stations capable of sustaining zero order torsionalacoustic waves, said method comprising the steps of: generating amodulating signal containing the information to be transmitted;establishing in said pipe zero order torsional acoustic waves which aremodulated according to a predetermined modulating mode by saidmodulating signal to contain the information to be transmitted and whichtravel from said transmitting station to said receiving station throughsaid intervening pipe length; and receiving said waves at said receivingstation to recover said signal and its contained information.
 2. Theacoustic communication method according to claim 1 wherein: said pipe isa drill string suspended from a drilling platform.
 3. The communicationmethod according to claim 1 wherein: said pipe is a drill stringsuspended within a well bore from a drilling platform; at least one ofsaid stations is located within said well bore; and said torsionalacoustic waves are induced in said drill string by driving said drillstring in torsional oscillation at frequencies within a selected rangeof frequencies.
 4. The acoustic communication method according to claim1 wherein: said pipe is a drill string suspended within a well bore froma drilling platform; said transmitting station is located within saidwell bore and said receiving station is located above said transmittingstation; and said torsional acoustic waves are established in said drillstring by driving said string in torsional oscillation at frequencieswithin a selected range of acoustic frequencies to launch said acousticwaves upwardly through said drill string to said receiving station. 5.The acoustic communication method according to claim 1 wherein: saidpipe is a drill string suspended within a well bore from a drillingplatform; said drill string is composed of a number of pipe sectionscoupled end to end by intervening couplings; and the acousticfrequencies of said torsional acoustic waves are related to the nominallength of said drill string sections in a manner such that said drillstring oscillates in at least one of its pass bands of torsionaloscillation.
 6. The acoustic communication method according to claim 5wherein: the acoustic frequencies of said torsional acoustic waves arerelated to the nominal length of said drill string sections in a mannersuch that said drill string oscillates in its base band of torsionaloscillation.
 7. The acoustic communication method of claim 1 wherein:said pipe is a drill string suspended within a well bore from a drillingplatform; said receiving station is located within said well bore; saidtransmitting station is located above said receiving station; and saidsignal is a command signal for effecting a selected function at saidreceiving station.
 8. The acoustic communication method of claim 1wherein: said pipe is a drill string suspended within a well bore from adrilling platform; said transmitting station is located within said wellbore and said receiving station is located above said transmittingstation; said communication method comprises the further step oftransmitting command signals through said drill string to saidtransmitting station; and said modulated acoustic waves are establishedin said drill string in response to said command signals.
 9. Acommunication system for communicating information betweensignal-transmitting and signal-receiving stations spaced along a pipehaving an intervening length between said stations capable of sustainingzero order torsional acoustic waves, said system comprising: means forgenerating a modulating signal containing the information to betransmitted; means for establishing in said pipe zero order torsionalacoustic waves which are modulated by said modulating signal to containthe information to be transmitted and which travel from saidtransmitting station to said receiving station through said interveningpipe length; and receiving means coupled to said pipe at said receivingstation for receiving said modulated waves to recover said signal andits contained information.
 10. An acoustic communication systemaccording to claim 9 wherein: said pipe is a drill string suspendedwithin a well bore from a drilling platform; and at least one of saidstations is located within said well bore.
 11. An acoustic communicationsystem according to claim 10 wherein: said means for establishing saidacoustic waves comprises a torsional wave transducer coupled to saiddrill string for inducing in said drill string torsional acoustic wavesof zero order.
 12. A communication system according to claim 9 wherein:said pipe is a drill string suspended within a well bore from a drillingplatform; said drill string is composed of a number of pipe sectionscoupled end to end by intervening couplings; and the acousticfrequencies of said torsional acoustic waves are related to the nominallength of said drill string sections in a manner such that said drillstring oscillates in at least one of its pass bands of torsionaloscillation.
 13. An acoustic communication system according to claim 11wherein: said drill string is composed of a number of pipe sectionscoupled end to end by intervening couplings; and said transducer isadapted to be driven to produce in said drill string torsional acousticwaves related to the nominal length of said drill string sections in amanner such that said drill string oscillates in at least one of itspass bands of torsional oscillation.
 14. An acoustic communicationsystem according to claim 13 wherein: said drill string is composed of anumber of pipe sections coupled end to end by intervening tool joints;and the acoustic frequencies of said torsional acoustic waves arerelated to the nominal length of said drill string sections in themanner such that said drill string oscillates in its base-band oftorsional oscillation.
 15. An acoustic communication system according toclaim 9 wherein: said pipe is a drill string suspended within a wellbore from a drilling platform; said transmitting station is locatedwithin said well bore and said receiving station is located above saidtransmitting station; and said means for establishing said acousticwaves comprises an electrical transducer coupled to said drill stringand adapted to be energized by an electrical driving signal to launchsaid acoustic waves upwardly through said drill string to said receivingstation.
 16. An acoustic communication system according to claim 9wherein: said pipe comprises a drill string suspended within a well borefrom a drilling platform; one of said stations is located within saidwell bore; said drill string includes a drilling kelly at the upper endof said string; and said means for receiving said acoustic wavescomprise an electroacoustic transducer embodied in said kelly.
 17. Anacoustic communication system according to claim 16 wherein: saidtransducer comprises a magnetostrictive transducer including a tubularmagnetostrictive body of non-circular cross-section forming the body ofsaid kelly.
 18. An acoustic communication system according to claim 17wherein: said Transducer includes field conductors to be energized bythe incident acoustic waves; a swivel rotatably connected to the upperend of said kelly for attachment to a hoist in said drilling platform;an electrical cable extending from said swivel for connection to saidreceiving means; and rotary electrical contacts on said kelly and swivelelectrically connecting said transducer conductors and cable.
 19. Anacoustic communication system according to claim 18 including: means onsaid swivel for conducting drilling mud to a chamber within said swivel;and said kelly having a central mud passage extending through saidtransducer body and communicating said chamber to the mud passage insaid drill string.
 20. An acoustic communication system according toclaim 9 wherein: said pipe is a drill string suspended within a wellbore from a drilling platform; and said means for establishing saidacoustic waves comprises an electroacoustic transducer having a tubularbody coupled in and forming a section of said drill string.
 21. Anacoustic communication system according to claim 20 wherein: saidtransducer body has a central mud passage forming a section of the drillstring mud passage.
 22. A method of communicating information betweensignal-transmitting and signal-receiving stations spaced along a drillpipe having a drill bit at the lower end thereof and having anintervening length between said stations capable of sustaining zeroorder torsional acoustic waves, said method comprising the steps of:generating an information signal representing and containing saidinformation, and which is other than the acoustic vibration that occursnaturally in the drill pipe due to grinding of the drill bit on the holebottom during the drilling operation; establishing in said drill pipezero order torsional acoustic waves which represent said informationsignal and contain the information to be transmitted and which travelfrom said transmitting station to said receiving station through saidintervening pipe length; and receiving said waves at said receivingstation and recovering therefrom said information signal and itscontained information.
 23. A communication system for communicatinginformation between signal-transmitting and signal-receiving stationsspaced along a drill pipe having a drill bit at the lower end thereofand having an intervening length between said stations capable ofsustaining zero order torsional acoustic waves, said system comprising:means for generating an information signal representing and containingsaid information, and which is other than the acoustic vibration thatoccurs naturally in the drill pipe due to grinding of the drill bit onthe hole bottom during the drilling operation; means for establishing insaid pipe zero order torsional acoustic waves which represent saidsignal and contain the information to be transmitted and which travelfrom said transmitting station to said receiving station through saidintervening pipe length; and receiving means at said receiving stationfor receiving said waves and recovering therefrom said signal and itscontained information.